1. Field of the Invention
The present invention relates generally to multi-drop type bus line system. More particularly, this invention relates to impedance matching a transmission line and a load in a multi-drop bus line system for transmitting a control signal. Still more particularly, this invention relates to a connector for a terminal in such a system, wherein the connector includes a switch actuated each time a cable is attached to the connector to alter the impedance of the terminal.
2. Description of the Prior Art
A so-called multi-drop type bus line system is known in which a plurality of terminals operable asychronously with one another are connected to the same information bus line. Information is interchanged among the respective terminals through the information bus line. The information might be transmitted and/or received in the form of a differential signal in order to increase the ability of the system to cope with noise, as is disclosed, for example, in U.S. Pat. No. 4,429,384.
FIG. 1 illustrates an example of the bus structure of such a conventional multi-drop type bus line system.
In this example, representative terminals (n-1), (n), (n+1) and (n+2) are connected to the same bus line BL as shown in FIG. 1. When the characteristic impedance of a bus line and an impedance of a load connected to the bus line are different in a communication system using such an information bus line, a standing or reflected wave occurs so that waveform distortion occurs. To avoid this shortcoming, an impedance matching circuit is frequently connected to the terminal portion of the bus line.
A method is also known which can prevent the standing wave from being produced by inserting the terminal impedance into a transmission line such as a feeder, a coaxial cable or the like, through which a high frequency signal is transmitted. However, such a technique is not sufficiently developed that the occurrence of the standing wave can be prevented in the information or bus line through which the above-mentioned information signal is transmitted.
Thus, it is a continuing problem in the art to provide simple and convenient impedance matching in a common bus system having many terminals, to prevent standing waves.